1. Field of the Invention
The present invention relates to a TV lens equipped with a still-taking function; and, in particular, to a TV lens, having a still-taking function, attachable to the main body of a broadcasting TV camera mounted with a color-decomposing prism or the like.
2. Description of the Prior Art
In general, a broadcasting TV camera or the like is configured such that, for yielding a color image with a high image quality, a three-color-decomposing prism and CCDs corresponding to the respective color light components for obtaining object information carried by the decomposed individual color light components are mounted in the TV camera main body, whereas various kinds of lenses meeting the aimed purpose, such as zoom lens and macro lens, are made attachable to the front end of the TV camera main body.
In the middle of live TV broadcasting of a sports event or taking a video of a wedding ceremony, there is a demand for electrically recording a highlight scene such as a goal scene or a wedding-cake-cutting scene as a still image by the TV camera (including a video camera, ditto hereinafter) being used.
In order to fulfill such a demand, one frame of the moving picture electrically taken by the TV camera may be used as a still image. When preference is given to the compatibility with current NTSC signals, however, then thus obtained still image would exhibit a lower image quality.
Therefore, it is preferred that a TV lens section or TV camera main body be mounted with a dedicated image-capturing system for still images, such that the still images are obtained with a better image quality by the imaging system separate from the TV-image-capturing system, whereas a part of the TV lens section is commonly used for the still-image-capturing system, so as to make the whole apparatus more compact at a lower cost.
On the other hand, since the TV-image-capturing system is designed such that each kind of aberration becomes favorable in both optical systems of the TV lens section and TV camera in total, when only a part of the TV lens section is commonly used for the still-image-capturing system, then a problem may occur in terms of aberration in the still-image-capturing system, causing a great task to improve.
In order to overcome such a problem, it is an object of the present invention to provide a TV lens additionally equipped with a still-image-capturing function, in which aberration is favorably corrected in optical systems of both of its TV-image-capturing system and still-image-capturing system in a simple and compact configuration.
On the other hand, when a lens section is commonly used for the TV-image-capturing system and the still-image-capturing system, it is necessary for a reflecting mirror or the like to divide a luminous flux or switch advancing directions of the luminous flux. However, it is not always easy to provide a space on the optical axis in which means for dividing the luminous flux or means for switching luminous flux directions, such as a reflecting mirror, can be inserted, while using the existing lens section.
In order to overcome such a problem, it is an object of the present invention to provide a TV lens additionally equipped with a still-image-capturing function, in which a part of an optical system is commonly used for its TV-image-capturing system and still-image-capturing system, and a space for inserting means for dividing a luminous flux or means for switching luminous flux directions used for guiding the incident luminous flux to both of the capturing systems can easily be secured.
Also, in the case where a dedicated electronic still camera for still images is attached to the TV lens section, when a part or all of the TV lens section is used for the still-image-capturing system so that the lens section is commonly used for the still-image-capturing system and TV-image-capturing system, since the electronic still camera has already been equipped with a taking lens, the two image-capturing systems may have composite focal lengths different from each other depending on the focal length of the taking lens of the electronic still camera. As a result, the angle of view may vary on the respective image-capturing devices of the two systems. Since the TV-image-capturing system is usually adjusted such that the picture size of its image-capturing device and the imaging size of the object image coincide with each other, if the respective image-capturing devices of both systems have the same picture size, then there will occur an inconvenience in the still-image-capturing system in that the picture size of the image-capturing device and the imaging size of the object image do not coincide with each other.
Further, when the respective image-capturing devices of the above-mentioned both systems have picture sizes different from each other, then there is a possibility that the disparity between the picture size of the image-capturing device and the imaging size of the object image in the still-image-capturing system may further increase.
In order to overcome such a problem, it is an object of the present invention to provide a TV lens additionally equipped with a still image capturing function, in which the respective angles of view of the optical systems on the image-capturing devices of both of the TV-image-capturing system and the still-image-capturing system can coincide with each other in a simple and compact configuration.
Meanwhile, when capturing a still image, it is necessary that a part of temporally continuous object scenes be cut out with a shutter.
While an electronic shutter for changing the charge storage period of a CCD by altering the bias level or drive clock has been known, when the electronic shutter is employed, then smear may be enhanced by the light irradiated on the light-receiving surface of the CCD in the shutter-off state, whereby the image quality may deteriorate.
Though the occurrence of smear has recently been suppressed due to the development of vertical over-drain and np substrates as compared with the conventional level, further improvement is desired for those requiring a high image quality.
Therefore, it is also an object of the present invention to provide a TV lens equipped with a still-taking function, in which there is no risk of smear being increased by light irradiating the light-receiving surface of the still-image-capturing device during the period in which the electronic shutter is closed.
Also, for example, when an electronic shutter is used in the case where the signal transmission system of the still-image-capturing device is of an interlacing type in conformity with NTSC or the like, then the charge storage periods of first and second fields constituting one frame shift from each other by 1/60 second. As a consequence, in an object moving fast in particular, the first field picture and the second field picture may shift from each other, whereby blurring may occur when a frame image is constructed.
In view of such circumstances, it is also an object of the present invention to provide a TV lens equipped with a still-taking function, which is free from blurring between two field images when the signal transmission system of its still-image capturing device is of an interlacing type.